How does Stevenson make Dr Jekyll and Mr Hyde's relationship so fascinating?

One major way in which Stevenson makes the relationship between Dr. Jekyll and Mr. Hyde so fascinating is through his use of point of view.  Stevenson employs a third-person limited omniscient perspective; this means that the narrator is not a participant in the story and can report the thoughts and feelings of only one character, and, in this case, that character is Mr. Utterson, Dr. Jekyll's lawyer and friend.  Because we can only learn about events based on what Mr. Utterson sees and hears, the truth about the relationship between Dr. Jekyll and Mr. Hyde remains a mystery to which clues are only revealed bit by bit.  We are put into Utterson's position by being just as in the dark and confused as he is, and so our interest is piqued just as Utterson's is.  Were the story written from Dr. Jekyll's perspective, there would likely be nowhere near as much mystery, and thus we would not find the relationship nearly as fascinating.